1. Field of the Invention
The present invention relates to a pulse wave measuring apparatus, and more particularly, to a pressurization type pulse wave measuring apparatus measuring a pulse wave by pressing a pressure sensing section including a pressure sensing surface to a human body.
2. Description of the Prior Art
A pressurization type pressure measuring apparatus has been generally known in which a contact pressure between a measuring object and a pressure sensitive surface is measured by applying a pressure to the measuring object. A pulse wave measuring apparatus is an application of the pressurization type pressure measuring apparatus. A pulse wave measuring apparatus measures a wave pulse by pressing a substrate having a pressure sensing means to surface of a human body in measurement of the pulse wave generated in an artery located in shallow depth under the skin of a human body. It is very important to measure a pulse wave of a patient using such a pulse wave measuring apparatus in order to be familiar with a health condition of the patient.
In the pressurization type pulse wave measuring apparatus, it is general to use a semiconductor pressure detecting apparatus equipped with a strain gauge or a diaphragm as a pressure sensing means. In this case, a pressure sensing section is configured so that a pressure sensing means for sensing a pulse wave is located on a surface of a housing mounted to a human body. As a literature concerning this kind of a pressurization type pulse wave measuring apparatus, there can be named JP-A 63-275320 (patent literature 1).
In a pressurization type pulse wave measuring apparatus, there has remained a problem that a substrate on which a pressure sensing means is formed is broken with ease. Since, as a pressure sensing means, generally, a semiconductor pressure detecting apparatus is used, a semiconductor substrate is used as a substrate. A thickness of the semiconductor substrate is usually on the order in the range from 100 μm to 300 μm and in a case where a diaphragm is used as a pressure sensing element, a thickness of a diaphragm portion is very thin on the order in the range of from 4 μm to 10 μm. Hence, if an external force is imposed on a main surface of the semiconductor substrate, a case arises where cracking and chipping occurs on the semiconductor substrate. In a case where such cracking or chipping occurs, a pulse wave cannot be measured and a trouble occurs in the pulse wave measuring apparatus.
It is mainly in the non-measurement stage that an external force so strong that cracking and chipping occur on a semiconductor substrate is imposed on the semiconductor substrate. Since, in the measurement stage, a human body surface is pressed by a pressure sensing section with a proper pressure, there arises no worry for cracking and chipping to occur on a semiconductor substrate. In the non-measurement stage, however, the pressure sensing surface is aligned face to face with the plane including the edge of an opening provided in the housing; therefore, a user has had a chance to get in touch with the pressure sensing surface, thereby having resulted in breakage of the semiconductor substrate.
While a main surface of a semiconductor substrate is usually covered with a passivation film, such a protective film has no function to protect a pressure sensing surface sufficiently against an external force. Furthermore, a pulse wave measuring apparatus has been available in which a protective film such as a rubber film covers a pressure sensing surface, whereas a thickness thereof is suppressed to a value of the order in the range of from 50 μm to 400 μm because of reduction in detection accuracy in the measurement stage. Therefore, such protective films including a rubber film exert no sufficient protective function against an external force.
In a pressurization type pulse wave measuring apparatus, a pressure sensing section including a pressure sensing surface is mounted inside of a housing so as to be movable upwardly and downwardly. Accordingly, a mounting strength of the pressure sensing section to the housing is not so high as expected. Hence, there is also a fear that amounting portion of the pressure sensing section is broken if a great external force in a lateral direction acts on the pressure sensing section.